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Twitter's IPO offers a reassuring message on U.S. innovation.

Nov. 7, 2013 7:05 p.m. ET

Twitter, an unprofitable but highly popular social-media service, went public Thursday on the New York Stock Exchange. Opening above $45 and then climbing to nearly $50 before closing at $44.90, the shares delivered a one-day gain of more than 70% for those lucky enough to buy at the $26 initial offering price. But Twitter's big day on the Big Board counts as good news for all Americans, whether or not they choose to invest.

Thursday's reassuring message is that the United States—Silicon Valley in particular—continues to...